[lldb] [test] Add a minimal test for x86 dbreg reading

[mgorny]

Summary

Add a test verifying that after the 'watchpoint' command, new values
of x86 debug registers can be read back correctly. The primary purpose
of this test is to catch broken DRn reading and help debugging it.

[labath]

I have a feeling we discussed this already, but I don't remember what was the conclusion.

Was exposing debug registers to the user a conscious choice? Other OSes don't actually do that. Neither does gdb, afaict...

In think that allowing the user to see dr contents is a good idea -- allows him to check what the debugger has done. I'm not convinced about the writing aspect though -- seems like an easy way to confuse the debugger and make it crash...

lldb/test/Shell/Register/x86-db-read.test

2

Who sets can-set-dbregs ?

[mgorny]

In D91264#2390699, @labath wrote:

I have a feeling we discussed this already, but I don't remember what was the conclusion.

Was exposing debug registers to the user a conscious choice? Other OSes don't actually do that. Neither does gdb, afaict...

In think that allowing the user to see dr contents is a good idea -- allows him to check what the debugger has done. I'm not convinced about the writing aspect though -- seems like an easy way to confuse the debugger and make it crash...

I agree with this. Hence, I've covered only the reading part. I don't have a strong opinion whether we should ban writes.

lldb/test/Shell/Register/x86-db-read.test

2

https://github.com/llvm/llvm-project/blob/master/lldb/test/Shell/lit.cfg.py#L123

[labath]

lldb/test/Shell/Register/x86-db-read.test

2

The feature name is dbregs-set, is it not ?

[mgorny]

Corrected REQUIRES.

[mgorny]

lldb/test/Shell/Register/x86-db-read.test

2

Indeed it is. Silly me.

[mgorny]

Restrict the test to FreeBSD only.

lldb/test/Shell/Register/Inputs/x86-db-read.cpp

+#include <cstdint>
+#include <csignal>
+
+uint8_t g_8w;
+uint16_t g_16rw;
+uint32_t g_32w;
+uint32_t g_32rw;
+
+int main() {
+  ::raise(SIGSTOP);
+  return 0;
+}

lldb/test/Shell/Register/x86-db-read.test

+# XFAIL: system-windows
+# REQUIRES: native && (target-x86 || target-x86_64) && can-set-dbregs
+# RUN: %clangxx_host -g %p/Inputs/x86-db-read.cpp -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+process launch
+# CHECK: Process {{[0-9]+}} stopped
+
+watchpoint set variable -w write g_8w
+# CHECK: Watchpoint created: Watchpoint 1: addr = 0x{{[0-9a-f]*}} size = 1 state = enabled type = w
+watchpoint set variable -w read_write g_16rw
+# CHECK: Watchpoint created: Watchpoint 2: addr = 0x{{[0-9a-f]*}} size = 2 state = enabled type = rw
+watchpoint set variable -w write g_32w
+# CHECK: Watchpoint created: Watchpoint 3: addr = 0x{{[0-9a-f]*}} size = 4 state = enabled type = w
+watchpoint set variable -w read_write g_32rw
+# CHECK: Watchpoint created: Watchpoint 4: addr = 0x{{[0-9a-f]*}} size = 4 state = enabled type = rw
+
+print &g_8w
+# CHECK: (uint8_t *) $0 = [[VAR8W:0x[0-9a-f]*]]
+print &g_16rw
+# CHECK: (uint16_t *) $1 = [[VAR16RW:0x[0-9a-f]*]]
+print &g_32w
+# CHECK: (uint32_t *) $2 = [[VAR32W:0x[0-9a-f]*]]
+print &g_32rw
+# CHECK: (uint32_t *) $3 = [[VAR64RW:0x[0-9a-f]*]]
+
+register read --all
+# CHECK-DAG: dr0 = [[VAR8W]]
+# CHECK-DAG: dr1 = [[VAR16RW]]
+# CHECK-DAG: dr2 = [[VAR32W]]
+# CHECK-DAG: dr3 = [[VAR64RW]]
+# CHECK-DAG: dr6 = 0x{{(00000000)?}}ffff0ff0
+# CHECK-DAG: dr7 = 0x{{(00000000)?}}fd7104aa
+
+process continue
+# CHECK: Process {{[0-9]+}} exited with status = 0